Recently, touch panels have been attracting attention. Touch panels have primarily been applied to small-sized devices including portable digital assistants (PDAs), mobile phones, etc. However, it is considered that there will be a trend toward touch panels that are larger in size as such touch panels are applied more to personal computer displays, etc.
In view of such a future tendency, electrodes according to the background art have a large electric resistance because the electrodes are made of indium tin oxide (ITO). Therefore, as the sizes of touch panels that are used in applications become larger, the signal waveforms of currents flowing between the electrodes tend to have blunt edges, resulting in a problem in which the response speed (the elapsed time after a fingertip has touched the touch panel and until the touched position is detected) becomes lower.
It has been known to lower the surface resistance of a touch panel by constructing electrodes to have a number of juxtaposed grids made up of thin lines of metal (metal thin lines). Furthermore, in order to suppress a moire phenomenon caused by a regular pattern of grids, there have been proposed electroconductive films having a random pattern of metal thin lines (see, for example, Japanese Laid-Open Patent Publication No. 2011-513846 (PCT), Japanese Laid-Open Patent Publication No. 2012-181815, and Japanese Laid-Open Patent Publication No. 2012-119163).
The electroconductive film disclosed in Japanese Laid-Open Patent Publication No. 2011-513846 (PCT) includes mesh bars, which are connected respectively to a plurality of terminals, and line zones (electrically insulated zones) disposed between the mesh bars. In particular, the mesh bars include a plurality of randomly shaped cells.
The electroconductive film disclosed in Japanese Laid-Open Patent Publication No. 2012-181815 includes transparent electrode pattern portions and transparent insulation pattern portions, which are laid out alternately on the surface of a base, thereby reducing differences between optical properties of areas where the transparent electrode pattern portions are present and areas where the transparent electrode pattern portions are not present (i.e., areas where the transparent insulation pattern portions are present), and preventing the transparent electrode pattern portions from being visually perceived. Moreover, plural lands are disposed randomly at spaced intervals in the transparent insulation pattern portions in order to suppress generation of moire patterns.
The electroconductive film disclosed in Japanese Laid-Open Patent Publication No. 2012-119163 comprises an electroconductive film having mesh-like line members disposed on a base. A structural pattern, which has a design different from the mesh-like pattern, is superposed on the electroconductive film. Thereafter, a convolution operation is performed on the power spectrum as viewed in plan and human standard visual response properties. Each of respective integral values within a special frequency band, which is equal to or greater than 1/4 times the spatial frequency corresponding to the average line width of the line members, and which is equal to or less than 1/2 times the special frequency, is larger than the integral value at a null spatial frequency. As a result, even if multiple electroconductive films are stacked for use in touch panel applications, for example, noise interference (in the form of moire patterns) is prevented from being produced.